System of television



NOV. 17, 1931. v TROUANT 1,832,672

SYS TEM OF TELEVI S I ON Filed Feb. 5. 1929 INVENTOR Virgil E. 7701102722 BY '4 v,

/ ATTORNEY Fig. 2.

' Patented Nov. 17, 1931 UNITED STATES PATENT OFFICE VIRGIL E. TROUANT, OF WILKINSBURG, IPENNSYLVANIA, ASSIGNOR T WESTINGHOUSE ELECTRIC 8c MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA SYSTEM OF TELEVISION Application filed February 5, 1929. Serial No. 337,589.

My invention relates to methods of employing radio-frequency currents in the transmission and reproduction of pictures and sounds.

One of the objects of my invention is to provide a system which shall enable a modulated electrical quantity of small power fluctuating many thousand times per second to generate a luminous flux of high intensity I 10 which shall faithfully reproduce said modulations.

Another object of my invention is to provide an efficient system by which an ordinary modulated broadcast wave may generate a luminous flux of high intensity which shall faithfully reproduce said modulations, and shall operate in doing so with a high luminous efliciency.

Another object of my invention is to provide a method by which a modulated nonelectrical quantity of small power may generate a luminous flux of high intensity, which shall faithfully reproduce the modulations of said non-electrical quantity.

A further object of my invention is to provide a system adapted to transform the energy of ordinary broadcast waves into light of high luminous efficiency and without the necessity of transmutation to other frequencies than those of the broadcast band.

Substantially all the present systems of transmitting pictures to a distance, and of recording sound through photographic agencies, produce their effects by modulating an electric current of relatively small power in accordance with a non-electrical quantity which it is desired to reproduce and cause this electric current to control a light flux as nearly as possible proportional in instantane- 40 ous magnitude to the fluctuations of the modulated electric current aforesaid. Since the light flux must, accordingly, fluctuate at a frequency of many thousands per second, it is practically necessary that it shall comprise 5 a gaseous discharge device, such devices being the only light source capable of varying in intensity with such extreme rapidity. Ordinary glow discharges have, however, certain undesirable qualities: first, they are of relatively low intrinsic brilliancy and, second, there is a sufficient total amount of light, the luminous a voltage drop at the cathode which is many times the voltage drop in the luminous column of the discharge. It is a consequence of the first of these defects that in order to obtain source must be of ver large dimensions; and it is a consequence of the second of these defects that in discharge tubes of any practicable size, almost the entire energy goes to overheat the cathode and only a very small remnant actually produces useful li ht. On the other hand it is highly desirable for many reasons that the light flux employed in systoms of the types under discussion shall come from a relatively small source of high intrinsic brilliancy and high luminous efliciency. The present low intensity glowdischarge devices of large size and oor efficiency are, therefore, highly unsatis actory.

It is also a characteristic of the television and photophone systems recently developed that they must take a, modulated control quantity of relatively small power and faithfully amplify it before it can be employed to modulate the light flux which they ultimately produce. In order that the amplified quantity shall be a faithful reproduction of the original, it is necessary that all components, whatever their frequency, present in the original shall be amplified in equal degree. It is practically impossible, however, todevise an amplifying system which shall magnify in equal degree all the components of the non-eleetrical quantity which it is desired to reproduce. Amplifier systems can be made which will amplify in substantially equal degree component currents of all frequencies comprehended within a considerable band above and below some predetermined base frequency; that is to say, an amplifier can be designed which will amplify in substantially equal degree'currents of all frequencies between limits of say, 50 kilocycles above and 50 kilocycles below a base frequency of 1,000 kilocycles. A band of frequencies 100,000 cycles wide is accordingly faithfully amplified by such an arrangement; whereas, it would be impossible to design an amplifier capable of magnifying in equal degree currents of all frequencies between zero and kilocycles, although as will be noted the total range of the frequency band is no greater in the latter case than in the former.

In accordance with the well known principles of alternating current theory, if the amplitude of an alternating current of 1,000 kilocycles per second is modulated at a frequency between zero and 100 kilocycles per second, the resulting current can be resolved into two component currents, one having a frequency lying within the band between 900 and 1,000 kilocycles per second, and the other having a frequency lying within the band between 1,000 and 1,100 kilocycles per second. Since, as has been explained above, an amplifier can be designed which will faithfully amplify currents throughout such a band of frequency as has been last mentioned, it may be taken as a practical requirement that, if a control quantit undergoing modulations up to 100 kilocyc es per second is to be amlified, it shall first be combined as-has just been described, with a carrier frequency 0 the order of 1,000 kilocycles per second and shall then be put through an amplifier designed to transmit a band of frequencies 100 kilocycles wide in the neighborhood of the latter figure. It can, to be a consequence of the foregoing facts that there will be available for producing the desired light flux in a photo-electric system of the sort to which my invention is a plicable, a modulated alternating current of a frequency lying within the ordinary radio broadcast range.

The facts outlined above thus lay down certain requirements which it would be decidedly advanta eous if the luminous source to be controlled %y a television or photophone system could fulfill; namely, it must be adapted for direct energization by currents of broadcast frequency and must respond instantaneously and with substantial proportionality to the modulated fluctuations of the latter; for space economy, since space is ordinarily at an extremely high premium in such apparatus, the light flux should be generated at a high liminous efiiciency; and the light source itselfshould preferably be of high intrinsic brilliancy. As has been pointed out, the glow discharge tubes now employed signally fail to meet the foregoing conditions; but it will be seen that the arrangement which I am about to describe fulfills them very completely, and that the inherent properties of the various components of the resulting arrangement so fit them to conjoint operation that they constitute a combination which produces results not attainable with arrangements hitherto employed.

In accordance with my invention I employ as the luminous source of my systems a discharge tube enclosing gas at low pressure; and instead of providing it with the conaccordingly, be taken P ventional electrodes for conduction of current to said gas, I excite the tube to luminosity solely by the inductive effect of a winding carrying the high frequency modulated output of the amplifier system of the general character above described. It is essential, if luminosity is to be excited in the foregoing manner, that the inducing current shall be of extremely high frequency; and currents of the frequency ideal for amplification in accordance with the principles described above are also ideal for thus exciting liminosity. Furthermore, the luminous intensity of such a discharge tube follows instantaneously and faithfully the fluctuations of the amplifier output current. It has an intrinsic brilliancy many times that which can be produced without sputtering of the electrodes in any tube now known; and since the entire electrical energy goes into the excitation of luminosity in the gas and none is lost in voltage drop at an electrode surface, the

f electrical efficiency is many times higher than the conventional tube of the present art. Such a tube is accordingly adapted to fulfill completely the conditions imposed by the electrical characteristics of the aparatus which must be employed to control the luminous discharge, and is adapted to employ directly and without the necessity of any intermediate transformation the electrical output of such an amplifier system as is practically an indispensable component of arrangements of the character under discussion.

With the foregoing principles and objects of my invention in mind, the latter will be more fully understood upon reading the following specification taken in connection with the drawings, in which;

Figure 1 shows a photophone system embodying my invention and adapted to photographically record speech or music on a moving1 film in a manner well known in the art, an

Fig. 2 shows a television receiving system constructed in accordance with my invention.

Referring in detail to Fig. 1, a telephone transmitter 1 of conventional form controls the grid potential of a three-electrode amplifier tube 2 in a manner too well known to require further description here. A threeelectrode tube 3 is provided with circuit connections of a well known type adapted to cause it to produce high frequency electrical oscillations. AssumingI that sounds of frequency up to, say, 20 ilocycles per second, are impressed upon the microphone 1, the grid of tube 2 is caused to fluctuate in potential relative to the cathode at a corresponding frequency. As is well known, in the radio art, the plate current of the tube fluctuates at the same frequency but with a greater power intensity.

The oscillator tube 3 may be adjusted by means of the variable condenser 4 to generate oscillations of a frequency of the order of, say 1,000 kilocycles per second. The flow of plate current to the tube 2 will cause a modulation of the high frequency currents generated by the tube 3, such modulation being at the frequency of the sounds impressed upon the microphone 1. Under the conditions just described, the current in the primary winding of the output transformer 5 may be 0011- sidered to be made up of two currents in addition to the unmodulated carrier current, one falling in a frequency hand between 1,000 and 1,020 kilocycles per second and the other falling within a frequency hand between 980 and 1,000 kilocycles per second.

The secondary of the output transformer 5 may be connected as the input element of an amplifier comprising three-electrode tubes 6 and 7 of conventional form. The variable condensers 8 and 9 in the grid circuits of tubes 6 and 7 may be adjusted to permit the transmission of the input band 980 to 1,000 kilocycles derived from transformer 5. \Vhile the amplifier system has been described as a transformer coupled, it will be recognized that any suitable amplifier arrangement known in the art may be employed; and that the number of stages may be varied to suit actual operating conditions met in any particular case.

The output circuit of tube 7 contains the variable condenser 10 and a coil 11 in shunt thereto and this local circuit may be tuned to the same frequency as the input circuits of the amplifier. The coil 11 is placed in good inductive relation to an enclosing bulb 12 which may be of glass, exhausted by methods well known in the art and provided with an atmosphere of gas at a suita le pressure. For instance, I have found a spherical bulb four inches in diameter enclosing neon at a pressure of one millimeters mercury to be suitable for many purposes, and to operate satisfactorily when the coil 11 is of ampere turns at a frequency of 4,800 kilocycles per second. The bulb 12 preferably contains no metallic electrodes. Other gases that may be employed are argon, helium and mercury vapor.

It will be found that the modulated high frequency current circulating in the winding 11 induces a glow discharge of high intrinsic brilliancy in the bulb 12 and that this discharge varies in instantaneous and faithful response to the modulation of the current in winding 11 consequent upon the variations in the output current from telephone transmitter 1.

While numerous optical systems in which the light flux from the bulb 12 may be employed will be evident to those skilled in the art, Figure 1 shows as a specific example a diaphragm 13 having a central opening which transmits light through the lens 14 on to a slit 15 in a screen 16. Immediately behind the slit 15 is positioned a moving film 17 mounted in a manner well known in the photophone art. As the film 17 moves past the slit 15, the fluctuations in intensity of the light from bulb 12 are recorded photographically; and after subsequent development, the film 17'may be employed to reproduce the sounds which were incident on transmitter 1 by means of systems well known in the photophone art.

It will be recognized that the precise method. of. employing the light flux from bulb 12 may be varied and that it may be used for many other purposes than photographt cally recording and reproducing sound, as briefly outlined here.

As another illustration of a system employing my invention, Fig. 2 shows an antenna 21, which impresses upon'a hot cathode amplifier tube 22, a received broadcast wave which may be the output of a television pic ture transmitter. The tube 22 may conveniently comprise a uni-potential cathode 23 maintained at operating temperature by a heater filament 24 and its anode 25 may be enclosed in a screen grid 26 in a manner well known in the radio tube art. The fluctuations in potential of grid 27, resulting from the input signal to antenna 21, are amplified by tube 22 and produce a current in the primary of transformer 28 which varies in accordance with such incoming signal. As a specific example, the incoming signal to antenna 1 may fluctuate with a periodicity of the order of 1,000 kilocycles a second.

It will be recognized that if the incoming signal to antenna 21 is not of a frequency adapted for anefficient or simple amplifier system, it may be changed in frequency by the employment of detectors or heterodyne systems embodying local sources of oscillations, in manners well known in the radio art. Thus piezo-electric crystals may be employed to causetube 22 to generate a local frequency subject to the modulation of grid 27.

Under the conditions above described, the current in the primary of transformer 28. will have a frequency suited to simple and efficient amplification and such frequency will be such as to most efficiently generate light in a bulb of the type of that described in connection with Fig. 1. The input circuits of amplifier tubes 31 and 32, which may, if

desired, be of the same form as tube 22, may

modulated current of a frequency near 1,000 kilocycles per second in the local circuit comprising variable condenser 35 and coil 36, in the output circuit of tube 32. Coil 36 is laced in inductive relation to an electrodeess bulb 37 of the same character as bulb 12 previously described. If desired, a pair of polished reflectors 38 and 39 may be positioned adjacent the bulb 37. The reflectors 38 and 39 may be connected to constitute an additional capacity in shunt to variable condenser 35 and they will induce a fluctuating electricfield through the gaseous atmosphere in bulb 37.

In the foregoing arrangement it will be readily evident that modulated high-frequency currents in coil 36 and, if used, the potential impressed onreflectors 38, 39 will produce a light flux in bulb 37, which will be modulated in substantial fidelity to the incoming broadcast waves incident upon antenna 21. The light emanating from. bulb 37 may be employed in numerous ways; for example, a rotating disc ll provided with a series of spirally disposed holes may be rotated in front of bulb 37 at a frequency synchronized by well known methods with that of a similar disc in the television transmitter. Anyone viewing the light of bulb 37 through the rapidly rotating holes in disc 41 will see a reproduction of the picture being transmitted from the television sending station.

It will be recognized that other specific arrangements for utilizing the light flux of bulb 37 for television reception or other purposes may be employed. Such arrangements are well known in the television art and their applicability in connection with applicants invention will be readily evident. It will also be recognizedthat numerous accessory arrangements, such as filters and other devices for suppressing undesired side bands and harmonics, and for maintaining a television receiving optical system in synchronism with that of the television sending station, may be employed in connection with my invention without departing from, or in many cases without in any way modifying, the principles thereof. It will also be evident that other forms of amplifiers than those specifically described here may be employed for that element of my arrangement.

While the coils 36 provide the preferable method of exciting discharge in bulb 37, it will be recognized that it may be desirable in certain instances to employ the plates 38 and 39 alone for such a purpose, the coils 36 being then removed to a distance and merely playing the part of a tuning inductance in the output circuit of the amplifier. It is also within the purview of my invention to provide the bulb 37 with auxiliary electrodes to supplement the purely inductive actions of coils 36 or blades 38 and 39. However, it is my present belief that the purely inductive arrangement shown in the drawings will be found preferable for most purposes. It is also within the purview of my invention to transform the frequency of the current being amplified at other stages of the amplifier than'the first as here described. In some instances, it will of course be unnecessary and undesirable to employ an amplifier of the original input power; but even in such cases it will usually result in more eflective operation if the exciting current of bulbs 12 and 36 is given a frequency of the order of 1,000 kilocycles. Hg. 1 embodies one system for transforming an input of power frequency into a modulated current of such frequency; and other methods are well known.

It is a valuable property of the inductively excited light source having the dimensions and structure already given as a specific example that the light generated seems to be much more exactly proportional at any time to the instantaneous current output from the amplifier than is the case with the conductively excited light sources of the present art, and believe this property, which is of the greatest practical value, to be characteristic of other atmospheres and dimensions also. Thelight flux can be arranged to be quite strictly proportional at all times to the instantaneous magnitude of the current in the inducing coil.

Many modifications of the principle of my invention will be evident to those skilled in the art and it is by no means limited to the specific embodiments here disclosed. I accordingly desire that the claims be given a broader interpretation, of which their terms are reasonably susceptible, taking into consideration the limitations as imposed by the prlor art.

I claim as my invention:

1. In combination with an input circuit energized by a modulated carrier current, an evacuated envelope containing a gas at reduced pressure, means for subjecting said envelope to the inductive influence of said modulated carrier current, and means for scanning said envelope.

2. In combination with an input circuit energized by a modulated carrier current, an evacuated spherical envelope containing a gas at reduced pressure, means for sub ecting said envelope to the inductive influence of said modulated carrier current, and means for scanning said envelope.

In testimony whereof. I have hereunto subscribed my name this 3lst day of January,

VIRGIL E. TROUANT. 

